An intact cytokinin-signaling pathway is required for Bacillus sp. LZR216-promoted plant growth and root system architecture altereation in Arabidopsis thaliana seedlings

Wide ranges of microorganisms found in rhizhosphere are able to regulate plant growth and development through production of phytohormones. However, little is known about the effects of these rhizobacteria on phytohormone cytokinin signal transduction in plants. We here found that Bacillus sp. LZR216 can promote growth and alter the root system architecture of Arabidopsis. To study the roles of cytokinin in this process, we used a series of cytokinin signaling mutants. We found that LZR216 inoculation exhibited little effects on the growth promotion and root development of the triple mutant ahp2,3,5. However, LZR216 promoted the growth and altered the root system architecture of single and double mutants of the cytokinin receptor. Furthermore, LZR216 treatment decreased the ARR5-GUS expression in the shoot apical meristem, but increased the expression in root tips. Transcript analysis indicated that LZR216 down-regulates the expressions of AHK3/AHK4, AHP1, and ARR4/5/7/10/12/15 in shoots, but up-regulates the expressions of AHK3/AHK4, AHP1/AHP3, and ARR4/5/7/10/12/15 in roots. Collectively, LZR216 plays different roles in cytokinin signaling between roots and shoots in Arabidopsis, and an intact cytokinin-signaling pathway is necessary for LZR216-promoted plant growth and root system architecture alteration.